The present invention concerns a plate heat exchanger comprising at least one stack of plate elements which plate elements each one has a central heat transferring part and a surrounding edge part. The heat transferring parts of the plate elements are permanently joined with each other in a plurality of spaced apart points and delimit between each other flow spaces for at least two heat exchanging fluids. Each plate element is of a double wall construction and comprises two heat transferring plates of substantially the same size and pressed to substantially the same form which heat transferring plate are in contact with each other but allows a heat exchanging fluid that leaks out through a hole in the one heat transferring plate to be led between the heat transferring plates to the edge parts of the plate elements.
The present invention also concerns a plate heat exchanger for at least two heat changing fluids which heat exchanger is permanently joined with at least one sealing means and comprises at least one core of plates with heat transferring plates, at least two end plates as well as inlet organs and outlet organs for the heat exchanging fluids. The plate package includes alternating heat transferring plates and intermediate heat transferring plates between the alternating plates. Each alternating plate and one of two adjacent intermediate plates form a double wall unit.
WO, A1, 91/17404 shows a plate heat exchanger of the kind mentioned above. Alternating plates 15, 17, 19, 21 and intermediate plates 16, 18, 20, 22 alternate in the core of plates, see FIG. 4. Each alternating plate and one of the two adjacent intermediate plates form a double wall unit. Possible fluid leakage through any one of the plates may flow further between the plates in the double wall unit which is closest concerned and out into the environment and thereby being made visible.
Normally double wall units situated next to each other are brazed together among other places in those points where the corrugations on the heat areas of the double wall units are in contacts with each other in the core of plates. It has been evident that as a result of a high temperature and a high pressure one risks at the same time an unwanted joint of the unitary plates being parts of each double wall unit in the corresponding points, right before the contact points mentioned above, or at least in a large number of them. In this way the mentioned further flow between the plates in the closest concerned double wall unit is made difficult in case of fluid leakage.
The present invention has as an aim to create a plate heat exchanger comprising double wall units which after the brazing together of the core of plates do not show the draw backs mentioned above.
The plate heat exchanger according to the invention thus comprises at least one stack of plate elements which plate elements each one has a central heat transferring part and a surrounding edge part, the heat transferring parts of the plate elements being permanently joined with each other in a plurality of spaced apart points and delimit between each other flow spaces for at least two heat exchanging fluids and whereby each plate element being of a double wall construction and comprising two heat transferring plates of substantially the same size and pressed to substantially the same form which heat transferring plates are in contact with each other but allows a heat changing fluid which leaks out through a hole in the one heat transferring plate to be led between the heat transferring plates to the edge parts of the plate elements.
For each one of the said plate elements the said heat transferring plates are in close contact with each other except right before each one of at least one of the said points with the closest around situated areas.
For each one of the said plate elements the said heat transferring plates may be in close contact with each other except right before each one of the majority of the said points with the closest around situated areas.
Another form of execution of the plate heat exchanger according to the invention is aimed for at least two heat exchanging fluids, is permanently joined with at least one sealing means and comprises at least one core of plates with heat transferring plates, at least two end plates as well as inlet organs and outlet organs for the heat exchanging fluids. The core of plates includes alternating heat transferring plates and intermediate heat transferring plates between the alternating heat transferring plates.
Each one of the said heat transferring plates shows at least one central corrugation pattern with ridges and valleys, at least four flowing through openings forming an inlet channel and an outlet channel through the core of plates for each one of the fluids as well as at least one everything surrounding edge part.
Each one of the said alternating heat transferring plates and a first one of the two respective adjacent intermediate plates create, together with the said sealing means, a channel for flow of one of the heat exchanging fluids from one of the said flowing through openings in one end to another one of the said flowing through openings in the opposite end of the said channel whereby every other one of the said channels lead flow of a first one of the said fluids and at least one of the remaining channels leads flow of a second one of the said fluids so that the said inlet channels and outlet channels for the said first and second fluids respectively are in fluid communication with a first and a second set of channels respectively.
Each one of the said alternating heat transferring plates and said first one of the two respective adjacent intermediate plates create, together with the said sealing means, at least two bypass channels each one pairwise connecting flowing through openings situated right before each other whereby the one flowing through opening in every pair is situated in the said alternating heat transferring plate and the other one in said first intermediate heat transferring plate, in order to lead flow of one of the heat exchanging fluids in bypass by the said channel.
Each one of the said alternating heat transferring plates and a second one of the said two adjacent intermediate plates create a double wall unit formed in such a way that an area between the two plates may create a passage through which fluid leakage through a hole in one of the plates may be led out between the plates to the edge part of the double wall unit in order to be made visible from outside. The said sealing means seals around every pair of flowing through openings situated right before each other, one in the said alternating heat transferring plate and the other in the said second intermediate heat transferring plate in order to create channels through which the fluids may pass each one separately without entering said area between the plates.
For each one of the said double wall units the said ridges and valleys on the said alternating plate are in their whole respective areal extensions adapted to and in near contact with the said corresponding ridges and valleys on the said intermediate plate except right before each one of at least one of those points with closest around situated areas where the ridges and valleys on a double wall unit are in contact with the ridges and valleys on another double wall unit in the core of plates.
The said ridges and valleys on the said alternating plate may for each one of the said double wall units in all of their respective areal extensions be adapted to and in near contact with the said corresponding ridges and valleys on the said intermediate plate except right before each one of the majority of those points with closest around situated areas where ridges and valleys on a double wall unit are in contact with ridges and valleys on another double wall unit in the core of plates.